The insulin-like growth factor II (IGF-II) receptor has high affinity binding sites for the polypeptide IGF-II and glycosylated lysosomal enzymes. This unique receptor's key role in transporting lysosomal enzymes is well established, but the mechanism by which IGF-II-initiated signal transduction events are mediated by the IGF-II receptor is controversial. To help elucidate this mechanism, the objective of this project is to map the ICF-II binding site of the IGF-II receptor using two complementary approaches. First, purified 125I-IGF-II affinity-labelled receptors will be digested with endoproteinase Glu-C, then peptide regions of the receptor covalently attached to IGF-II will be isolated for sequencing. Second, cDNA clones encoding the IGF-II receptor's avian homolog, which does not bind ICF-II, will be isolated by screening chicken cDNA libraries with radiolabelled fragments of mammalian IGF-II receptor cDNAs. Sequence and mapping information as well as reagents obtained in those studies will be used to designate targets for site-directed mutagenesis of the mammalian receptor's IGF-II binding site and to design avian/mammalian receptor chimeras. Wild-type, mutant and chimeric receptors will be expressed in mammalian cells to assess IGF-II binding parameters, and to investigate structure-function relationships linking IGF-II binding to signal transduction.